To verify the applicability of 25 m cast-in-place steel spring floating slab track in urban express rail transit, the vehicle-track coupled dynamics model and numerical method of CRH6 and cast-in-place steel spring floating slab are established based on the vehicle-track coupled dynamics theory. Through simulation calculation, the coupled dynamics performance of cast-in-place floating slab track bed and train under fast driving conditions is simulated, -and the safety, comfort and stability of 25 m cast-in-place steel spring floating slab track bed are evaluated. The effect of cast-in-place floating slab length, thickness and support damping on the dynamic performance of the system is studied. The research results show that: The denser the vibration isolators are, the better the stability of the track bed itself; The variation of the thickness of the cast-in-place steel spring floating slab bed on the operational safety indicators and ride comfort indicators of the intercity electric multiple units are not large; increasing the thickness of the floating slab can slightly improve the running stability of the vehicle; When the intercity electric multiple units is running, the stability indicators, the comfort rate and other indicators all meet the limit, that is, the cast-in-place floating slab track can meet the requirements of urban express rail transit. The research results can provide support for the dynamic design of the cast-in-place steel spring floating slab track with a speed of 160 km and above. © 2021, Editorial Department of JVMD. All right reserved.